According to more recent prior art, taking a bending machine as an example, bending programs are controlled by a numerical-control programmer according to a program which can be prepared on a cheap personal computer.
The operating machine generally consists of a vertical bending press with an upper movable punch and a lower fixed die, both of which are V-shaped.
A robot is associated with the bending press and carries a gripping member which may be in the form of a jaw. The gripping member can perform translational movements along three axes and rotary movements controlled by respective numerically-controlled motors. These motors are controlled in turn by the program.
The programmer receives feedback signals from sensors with which the robot is provided and these indicate to the programmer the successive linear and angular positions assumed by the gripping member.
The sensors which emit the feedback signals are of the type known as "encoders". Sensors of this type do not detect the linear and angular positions with reference to origins which are fixed once and for all, but to origins which correspond on each occasion to the linear and angular positions at the start of the operation. In practice, these origins correspond to the linear and angular positions which the gripping member and the metal sheet held thereby assume when the sheet is positioned for the formation of a first bend of the program.
In carrying out known methods, care is taken by some means or another that the metal sheet is positioned correctly for the first bend to be carried out. This positioning does not, however, take account of the fact that the jaws or other gripping member of the robot may be engaged with the metal sheet at a point which differs to a certain extent from an ideal or theoretical gripping point. Once the metal sheet has been positioned correctly for the formation of the first bend, the robot follows the program correctly as regards the successive bends to be formed. Since the gripping member is not engaged with the metal sheet at the theoretical point, however, it may follow paths so different from those envisaged that, during successive manipulations, it knocks against various obstacles including, with disastrous results, the tools of the press. This problem is more serious the smaller the metal sheets to be bent, in which case displacements of the gripping member even by a few millimeters from its estimated path may be disastrous.